1. Field of the Invention
This invention relates to a method for the manufacture of regenerated synthetic resin products, particularly parts of regenerated synthetic resin for use in slide fasteners.
2. Description of the Prior Art
At present, the environmental problems of a global scale are posing a serious theme in need of an urgent solution throughout the world.
Among other measures proposed for the solution in question, the perfection of a recycling technique which encourages the decrease of the volume of waste and advances the cyclic use of natural resources has come to attract a close attention as an exceptionally important task.
Particularly, as respects the industrial waste, the law concerning the disposal of waste clearly stipulates that the person concerned should be held responsible for the disposal. Then, the law concerning the promotion of the reclamation of resources recommends, in order to lighten a load of treatment or disposal of the waste also in the production stage, using such materials as permit easy separation into components and allow simple reclamation of separated components, devising convenient structures for products, developing products using raw materials only in small amounts and fulfilling satisfactory functions, and developing unit products easy of mutual separation.
Factories specializing in the manufacture of slide fasteners of synthetic resin are yielding from their production lines large amounts of waste plastics including rejected products, scraps, and waste threads as industrial waste year after year. They incur huge expenses in the disposal of such waste plastics and, therefore, find the efficient utilization of these waste plastics as an all-important problem.
The slide fasteners which are made of synthetic resin, however, have a problem concerning the characteristics which they require to possess. In the case of the slide fasteners, for example, the characteristics such as various mechanical properties and durability to withstand a sliding motion of a slider which the component parts of slide fasteners require to possess are varied. In the regeneration of slide fasteners made of synthetic resin from waste plastics, the reclaimed raw materials inevitably suffer from decline of purity and degradation of quality and, as a result, fail to allow manufacture of products which fully satisfy the various characteristics which the slide fasteners require to possess. Particularly in the case of such thin linear components as multifilaments, the inclusion of minute extraneous particles in the waste plastics possibly results in causing breakage in the regenerated multifilaments. The slide fasteners, therefore, cannot be efficiently recycled from the same viewpoint as that of daily sundries like PET (polyethylene terephthalate) bottles.
Then, the slide fasteners are possessed of decorative factors besides their functional factors. They are required to be dyed in various colors to meet diversified consumers' needs. Particularly in recent years, the desirability of manufacturing slide fasteners numerous in color yet small in lot size has come to find enthusiastic recognition. In the case of the slide fasteners made of synthetic resins which have been regenerated from waste plastics, however, since the raw materials themselves are already colored with various pigments and dyes, it is generally difficult to manufacture products whose component parts are harmoniously and homogeneously colored. The slide fasteners of such synthetic resins as have been reclaimed from the waste plastics, therefore, are preferred to be simultaneously dyed in one and the same colors by means of the piece dyeing.
Even when newly produced synthetic resin materials (virgin materials) are used, however, since the individual component parts such as, for example, those used in fastener tape fibers and those used for the formation of coupling elements, are different in kind of synthetic resin and in kind and quantity of pigment, the fastener tapes and the coupling elements during the course of piece dyeing manifest difference in ability to absorb dye. In the case of an injection molded fastener, since the yarns used for forming the fastener tapes have been drawn in the process of production and the material injected for forming the coupling elements has not been drawn and, therefore, they manifest a difference in degree of crystallization, the fastener tapes and the coupling elements during the course of piece dyeing betray a difference in ability to absorb dye. As a result, it is relatively difficult to dye simultaneously the individual component parts harmoniously and homogeneously. Worse still, it has been held that this simultaneous dyeing is impracticable when the injection molded fasteners are manufactured by using waste plastics as raw materials.